Doctor Yueh comes to see Paul who's on the mesage table following the shield practice with Gurney in the training room. Yueh informs Paul that there's no time for their regular lesson and that the Duke will be in to see him any moment, which excited Paul. He hadn't seen much of his father since the order to move to Arrakis. Yueh feels a sense of waste looking at Paul but reminds himself that he's doing this to save his wife. They talk about the lessons for Paul durring the trip; the Fremen, the storms and the worms. Yueh gives Paul an antique Bible as a gift and looses control when Paul accidentally reads Yueh's wife's favorite passage. We learn from Yueh's thoughts that he is involved with the Harkonnens and they have done something with his wife.

he's a traitor...House Atreides is greater than him..greater than his wife ...greater than any one person (including Leto) ...hes a narc little bitch ... there is no excuse...none...fuckin traitor ...he gets what he deserves

The way that Yueh is built as a traitor is actually one of the most impressive examples I've seen in literature. It's consistent HUMAN behaviour rather than consistent with what a 'character' in a story might do.